Front filter in plasma display panel

ABSTRACT

Disclosed is a front filter attached to a front surface of a plasma display panel, the front filter comprising: an antireflection coating for preventing reflection of incident light from outside; an optical characteristic film for improving optical characteristics of incident light from the panel, by decreasing brightnesses of red (R) and green (G) rays and by increasing brightness of blue (B) rays; an EMI shielding film for shielding emission of electromagnetic wave; and an NIR blocking film for blocking near infrared rays emitted from the panel, wherein, transmittance of emitted light from the plasma display panel when the emitted light transmits the antireflection coating, the optical characteristic film, the EMI shielding film, and the NIR blocking film is determined in dependence of wavelength of the emitted light, and wherein transmittance of B rays at a wavelength of 454 nm is 50-80%, transmittance of G rays at a wavelength of 525 nm is 40-80%, transmittance of orange rays at a wavelength of 580-592 nm is 5-30%, transmittance of R rays at a wavelength of 610-650 nm is 50-80%, and transmittance of NIR at a wavelength of 850-950 nm is 1-10%.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to a plasma display panel, moreparticularly, to a front panel attached to a front surface of the plasmadisplay panel.

2. Discussion of the Background Art

Principle of plasma display panel displays (hereinafter referred to asPDP) technology is that 147 nm-ultraviolet rays generated by dischargeof different compositions of inert gas mixtures, such as, He+Xe, Ne+Xeor He+Ne+Xe, irradiate phosphors emitting in either red, green, or blueto display images including characters or graphics. The PDP technologyis at mass production stage, and recent advances in PDP technologiesmade easier to manufacture thin PDPs and to provide much improvedpicture quality. Especially, in case of a three-electrode surfacedischarge type PDP, charge particles formed by discharge (i.e. wallcharge) are stacked on the surface, which in turn protect electrodesfrom sputtering originated by discharge. Thus, the three-electrodesurface discharge type PDP is known for low consumption of voltage andlong lifespan.

FIG. 1 is a perspective view of the structure of a discharge cell in arelated art PDP.

Referring to FIG. 1, the discharge cell of the related art PDP adoptingthe three-electrode surface discharge type structure includes a scanelectrode (Y) and a sustain electrode (Z) formed on an upper substrate10, and an address electrode (X) formed on a lower substrate 18. Thescan electrode (Y) and the sustain electrode (Z) respectively includestransparent electrodes (12Y and 12Z), and metal bus electrodes (13Y and13Z) formed on an edge of the transparent electrodes (12Y and 12Z) andhaving a smaller line width than that of the transparent electrodes (12Yand 12Z).

In general, the transparent electrodes (12Y and 12Z) are composed ofIndium-Tin-Oxide (ITO) and formed on the upper substrate 10. The metalbus electrodes (13Y and 13Z) are typically made of chrome (Cr) andformed on the transparent electrodes (12Y and 12Z), reducing voltagedrop caused by the highly resistive transparent electrodes (19Y and12Z).

Also, an upper dielectric layer 14 and a protective film 16 are layeredon the upper substrate 10 on which the scan electrode (Y) and thesustain electrode (Z) are formed side by side. The charge particlesformed by discharge (i.e. wall charge) are stacked on this upperdielectric layer 14. The protective film 16 protects the upperdielectric layer 14 from damages caused by sputtering during plasmadischarge, and increases ejection rate of secondary electrons. Usuallymagnesium oxide (MgO) is used for the protective film 16.

On the lower substrate 18 on which the address electrode (X) is formedis a lower dielectric layer 22 and a barrier rib 24. Surfaces of thelower dielectric layer 22 and the barrier rib 24 are coated with aphosphor layer 26. The address electrode (X) is formed at right anglesto the scan electrode (Y) and the sustain electrode (Z). The barrier rib24 is formed in a strip or lattice pattern, and prevents ultravioletrays and visible rays generated by discharge from leaking by an adjacentdischarge cell. The phosphor layer 26 is excited by ultraviolet raysgenerated by plasma discharge, and generates one of visible rays in red,blue, or blue.

The mixed inert gas is injected to discharge space formed in between theupper/lower substrate 10, 18 and the barrier rib 24.

To obtain continuous-tone images, each frame of PDP is divided into aplurality of subfields with different frequencies of the radiation intime-sharing system. Each subfield is composed of three parts: a resetperiod for resetting the full screen, an address period for selecting ascan line and for selecting a cell among the selected scan line, and asustain period for display images in gray scales according to thefrequency of discharge.

For instance, suppose that an images needs to be displayed in 256 grayscales. Then, as shown in FIG. 2, a frame period (16.67 ms)corresponding to 1/60 sec is divided into 8 subfields (SF1 through SF8).As described above, each of these eight subfields (SF1 though SF8) iscomposed of three parts, namely the reset period, the address period,and the sustain period. The reset and address periods of each subfieldate same for each subfield, but the sustain period of each subfield isexponentially increased at the rate of 2″ (n=0, 1, 2, 3, 4, 5, 6, 7).

Moreover, a front filter is installed at the upper substrate 10 of thePDP, to shield electromagnetic wave and to prevent reflection ofexternal light.

FIG. 3 is a cross-sectional view of one side of a related art PDP.

Referring to FIG. 3, the related art PDP includes a panel 32 for whichan upper substrate and a lower substrate are tightly adhered to eachother, a front filter 30 installed at the front surface of the panel 32,a heat radiation plate 34 installed at the rear surface of the panel 32,a printed circuit substrate 36 attached to the heat radiation plate 34,a back cover 38 for compassing the rear surface of the PDP, a filtersupporting part 40 for connecting the front filter 30 to the back cover38, and a bearing member 42 installed in between the front filter 30 andthe back cover 38 to compass the filter supporting part 40.

The printed circuit substrate 36 sends actuation signals to theelectrodes of the panel 32. To this end, the printed circuit substrate36 is mounted with diverse driving parts that ate not shown in FIG. 3.The panel 32, in response to the actuation signal provided from theprinted circuit substrate 36, displays a desired image. The heatradiation plate 34 radiates heat generated from the panel 32 and theprinted circuit substrate 36. The back cover 38 protects the panel 32from external impacts, and blocks ElectroMagnetic Interference(hereinafter referred to as EMI) in the rear surface.

The filter supporting part 40 electrically connects the front filter 30to the back cover 38. In other words, the filter supporting part 40earths the front filter 30 to the back cover 38, and prevents anoccurrence of EMI on the side. The bearing member 42 bears the filtersupporting part 40, the front filter 30, and the back cover 38.

The front filter 30 not only shields EMI but also prevents thereflection of external light. To this end, as shown in FIG. 5, the frontfilter 30 includes an antireflection coating 50, an opticalcharacteristic film 52, a glass 54, an EMI shielding 56, and a nearinfrared rays (hereinafter referred to as NIR) blocking film 58. Inreality, an adhesive intermediate film is formed in between adjacentfilms (50, 52, 54, 56, and 58) of the front filter 30. In addition, theoptical characteristic film 52 is not usually an independent separatelayer as shown in the drawing. Instead, the optical characteristic film52 is formed by infusing a specific material to the adhesiveintermediate film. The structure of the front filter 30 is slightlydifferent, depending on which manufacturer produces the front filter.For the convenience of description of the invention, the adhesiveintermediate film is not illustrated in the drawings. However, theoptical characteristic film 52 is well illustrated as a separate layer,and the structure of the front filter 30 is the one currently being usedin the PDP.

The antireflection coating 50 prevents the reflection of an incidentlight from outside and thus, improves contrast of images on the PDP. Theantireflection coating 50 is formed on the surface of the front filter30. In some cases, the antireflection coating 50 can be formedadditionally on the rear surface of the front filter 30 as well. Theoptical characteristic film 52 reduces the brightnesses of red (R) andgreen (G) rays among incident light from the panel 32 but increases thebrightness of blue (B) ray, thereby improving optical characteristics ofthe PDP.

The glass 54 protects the front filter 30 from external impacts. Inother words, the glass 54 supports the front filter 30 in order toprevent the front filter 30 and the filter 32 from being damaged byexternal impacts.

The EMI shielding film 56 shields EMI, and prevents the ejection of EMIincidented from the panel 32 to the outside.

The NIR blocking film 58 blocks NIR radiation from the panel 32, andusing an IR like a remote controller, it helps signal-transmittingdevices to able to do their work as normally by preventing an excess ofthe ejection of NIR to the outside more than what is required.

In the meantime, the EMI shielding film 56 and the NIR blocking film 58can be integrated together, instead of being separate layers.

Referring now to FIG. 5, the above described front filter 30 iselectrically connected to the back cover 38 through the filtersupporting part 40. To be more specific, the filter supporting part 40is connected to the both components in such manner that it covers formone end of the front filter 30 to the rear surface of the front filter30. Here, the filter supporting part 40 is electrically connected to atleast one of the EMI shielding film 56 and the NIR blocking film 58.That is, by earthing the front filter 30 to the back cover 38, thefilter supporting part 40 can shield the EMI and/or NIR effects.

Therefore, the glass 54 in the related art front filter 30 serves toprotect the front filter 30 from external impacts. However, one ofdisadvantages of using the glass 54 is that the thickness of the frontfilter 30 with the glass 54 is increased. In addition, when the glass 54is inserted to the front filter 30, total weight and cost of manufactureare increased.

To resolve the above problems, a film type front filter 60 without theglass 54 is newly introduced, as depicted in FIG. 6. The film type frontfilter 60 includes an antireflection coating 62, an opticalcharacteristic film 64, an EMI shielding film 66, and an NIR blockingfilm 68. An adhesive intermediate layer is formed in between adjacentfilms 62, 64, 66, and 68 of the film type front filter 60 to adhere thefilms to one another. In general, the optical characteristic film 60 isnot a separate layer, but formed by infusing a specific material to theadhesive intermediate layer. The structure of the front filter 60 isslightly different, depending on which manufacturer produces the frontfilter 60. For the convenience of description of the invention, theadhesive intermediate film is not illustrated in the drawings. However,the optical characteristic film 64 is shown as a separate layer.

The antireflection coating 62 is formed on the surface of the film typefront filter 60, and prevents the reflection of an external incidentlight back to the outside. The optical characteristic film 64 dims downred (R) and green (G) rays among incident light from the panel 32 butincreases the brightness of blue (B) ray, thereby improving opticalcharacteristics of the PDP.

The EMI shielding film 66 shields EMI, and prevents the ejection of EMIincidented from the panel 32 to the outside. The EMI shielding film 66can be integrated with the NIR blocking film 68 which will be discussednext.

The NIR blocking film 66 blocks the incidence of NIR from the panel 32.Here, NIR has a wavelength of 700-1200 nm, and is generated by Xe thatemits 800-100 nm rays during the discharge of mixed inert gases filledin the PDP panel. When the NIR is ejected to the outside,signal-transmitting devices like a remote controller for transmittingsignals via IR do not work. As a result, signals cannot be transmittedto the PDP any more. That is to say, the ejection of the NIR causesmalfunction of the remote controller. Hence, the NIR blocking film 68made of NIR absorbing materials (or colorant) prevents an excess of theejection of NIR to the outside more than what is required, to ensurethat signals from the remote controller for example are properlytransmitted to the panel 37.

The merits of the film type front filter 60 are that the film type frontfilter without the glass 54 is lighter and thinner than the front filterwith the glass 54. Also, the film type front filter 60 can reduce costof manufacture by not using the glass 54.

On the other hand, FIG. 7 shows a representative light transmittancecurve achieved with the related art film type front filter 60 and therelated art front filter 30 including the glass 54. Even though thetransmittance of such front filters is influenced by what kind ofcolorant is infused to each functional layer of the front filter andwhat kind of materials the functional layers are made of, it is moreheavily influenced by transmittance curve design for determiningtransmittance of the front filter.

Referring to FIG. 7, transmittance of orange rays at a wavelength of580-592 nm of the front filters 30 and 60 according to the related artis already close to 40%, and thus, color purity of the PDP displayingimages in A, G, and B colors is severely degraded. For instance, when itis necessary to express a white color using R, G, and B colors, ayellowish white is displayed instead, or it is sometimes difficult toexpress flesh color.

Furthermore, transmittance of green (G) rays 72 at a wavelength of 525nm is too much lower than transmittance of blue (B) rays 71 or red (R)rays 74.

Also, transmittance of NIR 75 causing malfunction of the remotecontroller is as much as 5-10%.

Therefore, there is a growing need for improvement of transmittancedesign of the front filter.

SUMMARY OF THE INVENTION

An object of the invention is to solve at least the above problemsand/or disadvantages and to provide at least the advantages describedhereinafter.

Accordingly, one object of the present invention is to solve theforegoing problems by providing a front filter having an idealtransmittance curve.

The foregoing and other objects and advantages are realized by providinga front filter a front filter attached to a front surface of a plasmadisplay panel the front filter comprising: an antireflection coating forpreventing reflection of incident light from outside; an opticalcharacteristic film for improving optical characteristics of incidentlight from the panel, by decreasing brightnesses of red (R) and green(G) rays and by increasing brightness of blue (B) rays; an EMI shieldingfilm for shielding emission of electromagnetic wave; and an NIR blockingfilm for blocking near infrared rays emitted from the panel wherein,transmittance of emitted light from the plasma display panel when theemitted light transmits the antireflection coating, the opticalcharacteristic film, the EMI shielding film, and the NIR blocking filmis determined in dependence of wavelength of the emitted light, andwherein transmittance of B rays at a wavelength of 454 nm is 50-80%,transmittance of G rays at a wavelength of 525 nm is 40-80%,transmittance of orange rays at a wavelength of 580-592 nm is 5-30%,transmittance of R rays at a wavelength of 610-630 nm is 50-80%; andtransmittance of NIR at a wavelength of 850-950 nm is 1-10%.

Another aspect of the invention provides a front filter attached to afront surface of a plasma display panel, the front filter comprising: anantireflection coating for preventing reflection of incident light fromoutside; an optical characteristic film for improving opticalcharacteristics of incident light from the panel, by decreasingbrightnesses of red (R) and green (G) rays and by increasing brightnessof blue (B) rays; an EMI shielding film for shielding emission ofelectromagnetic wave; and an NIR blocking film for blocking nearinfrared rays emitted from the panel, wherein, transmittance of emittedlight from the plasma display panel when the emitted light transmits theantireflection coating, the optical characteristic film, the EMIshielding film, and the NIR blocking film is determined in dependence ofwavelength of the emitted light, and wherein transmittance of B rays ata wavelength of 454 nm is 60-70%, transmittance of G rays at awavelength of 525 nm is 60-70%, transmittance of orange rays at awavelength of 580-592 nm is 5-20%, transmittance of R rays at awavelength of 610-630 nm is 60-70%, and transmittance of NIR at awavelength of 850-950 nm is 1-5%.

In an exemplary embodiment of the invention, the front filter furthercomprises a glass for protecting the front filter and the panel fromexternal impacts.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objects and advantages of the invention may be realizedand attained as particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in detail with reference to thefollowing drawings in which like reference numerals refer to likeelements wherein:

FIG. 1 is a perspective view of the structure of a discharge cell in arelated art PDP;

FIG. 2 illustrates a frame in 256 gray scales for used in a related artplasma display panel;

FIG. 3 is a cross-sectional view of one side of a related art PDP;

FIG. 4 is a cross-sectional view of the front filter in FIG. 3;

FIG. 5 is a detailed exploded view illustrating an earthing process onthe front filter in FIG. 3 and a filter supporting part;

FIG. 6 is a cross-sectional view of a related art film type frontfilter;

FIG. 7 illustrates a transmittance curve achieved with a related artfront filter;

FIG. 8 illustrates a transmittance curve achieved with a front filter inaccordance with a first preferred embodiment of the present invention;and

FIG. 9 illustrates a transmittance curve achieved with a front filter inaccordance with a second preferred embodiment of the present invention.

DETAILED DESCRIPTION OP PREFERRED EMBODIMENTS

The following detailed description will present a front filter in aplasma display panel according to a preferred embodiment of theinvention in reference to the accompanying drawings.

FIG. 8 illustrates a transmittance curve achieved with a front filter ina PDP according to a first preferred embodiment of the presentinvention.

Similar to the structure of a related art front filter, the front filterof the invention includes an antireflection coating, an opticalcharacteristic film, a glass, an EMI shielding film, and an NIR blockingfilm. If desired, the glass can be removed. The optical characteristicfilm and the NIR blocking film are not separate layers, and an adhesiveintermediate layer having a specific material is formed in between them.

Although transmittance of the front filter is influenced by what kind ofcolorant is infused to each functional layer of the front filter andwhat kind of materials the functional layers are made of, it is moreheavily influenced by transmittance curve designing for determiningtransmittance of the front filter.

Referring to the transmittance curve shown in FIG. 8, which is achievedwith the front filter according to the first embodiment of theinvention, transmittance of B rays 81 at a wavelength of 454 nm is50-80%, transmittance of G rays 82 at a wavelength of 525 nm is 40-80%,transmittance of orange rays 83 at a wavelength of 580-592 nm is 5-30%,transmittance of R rays 84 at a wavelength of 610-630 nm is 50-80%, andtransmittance of NIR 85 at a wavelength of 850-950 nm is 1-10%.

Compared to transmittance achieved with a related art front filter, thetransmittance of G rays 82 has been increased considerably by 20% to30%, resulting in a remarkable increase of color temperature, and thetransmittance of orange rays 83 has been reduced by 20-30%, resulting ina remarkable increased of color purity. Besides, by designing thetransmittance curve to have an increased slope at the NIR 85 wavelengthrange, manufacturers can greatly reduce the transmittance of NIR 85 thatis known to cause malfunction of a remote controller.

Therefore, the front filter according to the first embodiment of theinvention shows an ideal light transmittance curve, generating effectslike improvement of color purity of the PDP and increases of contrastand color temperature.

FIG. 9 illustrates a transmittance curve achieved with a front filter ina PDP according to a second preferred embodiment of the presentinvention.

In FIG. 9, a solid line indicates a spectral transmittance curve, and adotted line indicates a spectral emission curve obtained from lightemission from the PDP.

Referring to the transmittance curve shown in FIG. 9, which is achievedwith the front filter according to the second embodiment of theinvention, transmittance of B rays 91 at a wavelength of 454 nm is60-70%, transmittance of G rays 92 at a wavelength of 525 nm is 60-70%,transmittance of orange rays 93 at a wavelength of 580-592 nm is 5-20%,transmittance of R rays 94 at a wavelength of 610-630 nm is 60-70%, andtransmittance of NIR 95 at a wavelength of 850-950 nm is 1-5%.

In FIG. 9, a sharp absorption peak 96 is formed at 480-500 nm betweenthe G rays 92 and the R rays 94, and as a result thereof, the differencebetween the transmittances of B rays 91 and G rays 92 and thetransmittance at the wavelength range with the absorption peak 96 is10-20%.

Also, when a sharp absorption peak 96 is formed at 580-600 nm betweenthe G rays 92 and the R rays 94, the difference between thetransmittances of B rays 91 and G rays 92 and the transmittance at thewavelength range with the absorption peak 96 is 10-50%.

To achieve a noticeable reduction in NIR 95 transmission, a sharp NIRabsorption peak 97 can be formed at a wavelength of 640-700 nm, causingthe transmittance difference between the R rays 95 and the NIR 95 is1-70%.

Compared to transmittance achieved with a related art front filter, thetransmittance of G rays 92 has been increased considerably by 20% to30%, resulting in a remarkable increase of color temperature, and thetransmittance of orange rays 93 has been reduced by 20-30%, resulting ina remarkable increased of color purity. Besides, by designing thetransmittance curve to have an increased slope at the NIR 95 wavelengthrange, manufacturers can greatly reduce file transmittance of the NIR 95that is known to cause malfunction of a remote controller.

When the absorption peak 96 between the B rays 91 and the G rays 92 isat 480-500 nm, light transmittance at a wavelength range where colorpurity of rays is low is noticeably reduced, and color purities of the Brays and G rays are improved.

Therefore, the front filter according to the second embodiment of theinvention transmits only rays from a certain wavelength range wherecolor purities of R, G and B rays are light.

Moreover, color contrast effect can be increased by reducingtransmittance of other colored rays at different wavelength ranges fromthe wavelength ranges transmitting three-color rays emitted from PDPphosphors.

In conclusion, color purity of the PDP can be improved by manufacturingthe front filter to have the idea light transmittance curve.

While the invention has been shown and described with reference tocertain preferred embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

The foregoing embodiments and advantages are merely exemplary and arenot to be construed as limiting the present invention. The presentteaching can be readily applied to other types of apparatuses. Thedescription of the present invention is intended to be illustrative, andnot to limit the scope of the claims. Many alternatives, modifications,and variations will be apparent to those skilled in the art. In theclaims, means-plus-function clauses are intended to cover the structuresdescribed herein as performing the recited function and not onlystructural equivalents but also equivalent structures.

1-10. (canceled)
 11. A front filter, comprising: an antireflectioncoating for preventing reflection of incident light from outside; anoptical characteristic layer for improving optical characteristics ofincident light from a display panel; an EMI shielding film for shieldingemission of electromagnetic wave; and an NIR blocking layer for blockingnear infrared rays emitted from the display panel, wherein lighttransmittance of emitted light from the display panel when the emittedlight traverses the antireflection coating, the optical characteristiclayer, the EMI shielding film, and the NIR blocking layer is determinedindependent of wavelength of the emitted light, wherein lighttransmittances in whole wavelength ranges between green rays and redrays are less than light transmittances of the green rays and red rays.12. The front filter according to claim 11, wherein light transmittanceat a wavelength range between blue rays and the green rays is less thanlight transmittances of the blue rays and green rays.
 13. The frontfilter according to claim 11, wherein light transmittance of blue raysat a wavelength of 454 nm is 50-80%.
 14. The front filter according toclaim 11, wherein light transmittance of the green rays at a wavelengthof 525 nm is 40-80%.
 15. The front filter according to claim 11, whereinlight transmittance of orange rays at a wavelength of 580-592 nm is5-30%.
 16. The front filter according to claim 11, wherein lighttransmittance of the red rays at a wavelength of 610-630 nm is 50-80%.17. The front filter according to claim 11, wherein light transmittanceof near infrared rays at a wavelength of 850-950 nm is 1-10%.
 18. Thefront filter according to claim 11, wherein the front filter is attachedto a front surface of the display panel.
 19. The front filter accordingto claim 11, further comprising a glass for supporting and protectingthe front filer.
 20. A front filter, comprising: an antireflectioncoating for preventing reflection of incident light from outside; anoptical characteristic layer for improving optical characteristics ofincident light from a display panel; an EMI shielding film for shieldingemission of electromagnetic wave; and an NIR blocking layer for blockingnear infrared rays emitted from the display panel, wherein lighttransmittance of emitted light from the display panel when the emittedlight traverses the antireflection coating, the optical characteristiclayer, the EMI shielding film, and the NIR blocking layer is determinedindependent of wavelength of the emitted light, wherein lighttransmittance at a wavelength ranges between blue rays at a wavelengthof 454 nm and green rays at a wavelength of 525 nm is less than lighttransmittances of the blue rays and green rays.
 21. The front filteraccording to claim 20, wherein light transmittance at a wavelength rangebetween the green rays and red rays at a wavelength of 610-630 nm isless than light transmittances of the green rays and red rays.
 22. Thefront filter according to claim 20, wherein the light transmittance at awavelength range between the blue rays at a wavelength of 454 nm and thegreen rays at a wavelength of 525 nm is less than the lighttransmittances of the blue rays and green rays by 1-20%.
 23. The frontfilter according to claim 21, wherein the light transmittance at awavelength range between the green rays and red rays at a wavelength of610-630 nm is less than the light transmittances of the green rays andred rays by 10-50%.
 24. The front filter according to claim 20, whereinthe light transmittance of the green rays is 40-80%.
 25. The frontfilter according to claim 20, wherein light transmittance of the redrays at a wavelength of 610-630 nm is 50-80%.
 26. A front filtercharacterized of a light transmittance curve, wherein lighttransmittances in whole wavelength ranges between green rays and redrays are less than light transmittances of the green rays and red rays.27. The front filter according to claim 26, wherein light transmittanceat a wavelength range between blue rays at a wavelength of 454 nm andthe green rays at a wavelength of 525 nm is less than lighttransmittances of the blue rays and green rays.
 28. The front filteraccording to claim 26, wherein light transmittance of the green rays ata wavelength of 525 nm is 40-80%.
 29. The front filter according toclaim 26, wherein light transmittance of the red ray at a wavelength of610-630 nm is 50-80%.
 30. The front filter according to claim 27, lighttransmittance at a wavelength range between blue rays and green rays isless than light transmittances of the blue rays and green rays by 1-20%.